Of various interfaces available for interacting with a computer system, one of the easiest to use and understand is the touch screen. This technology allows a user to simply touch an icon or picture to navigate through the system, display the information the user is seeking, and to enter data. For this reason this technology is widely used in many applications, including desktop computers, tablet computers, mobile devices, bank machines, information kiosks, restaurants, cars, navigation systems, etc.
A number of different methodologies are used to implement touch screen technology, and each has advantages and disadvantages. These methodologies include resistive, capacitive, surface acoustic wave, infrared, and optical.
A contemporary infrared touch screen employs a plurality of light emitting diodes (LEDs), positioned along each axis of a display screen. Each LED emits a beam of light, which is projected across the display. A plurality of photo detectors is positioned on opposite sides of the screen for receiving the light beams from the LEDs. Thus the LED light beams create a matrix or grid of light beams. A touch on the screen blocks at least one light beam on each of the two axes from reaching its corresponding photo detectors. The location of the touch is determined based on a calculated intersection of the two or more obstructed light beams.
Infrared and other LED matrix touch screen input systems, however, suffer from numerous disadvantages. For example, a contemporary infrared touch screen input system has about 40 or more LEDs and photo detectors along each axis. Therefore these contemporary systems employ many discreet components, and these many components have to be connected to a controller. These many components and interconnections take up a lot of space around the perimeter of a display, making it difficult to incorporate such systems into displays and particularly small displays, such as displays in hand held devices. Another problem is that due to the large number of components needed, the technology is more susceptible to individual component failures. Failures can cause the touch screen to stop functioning partially or fully. In addition, the high number of components tends to make such touch screen input devices very complicated and expensive. A further consideration is the power consumption of a touch input system. Systems having a lot of components, for example one or more arrays of LEDs, require more power to operate all the components. Another problem of this type of technology is that it provides for relatively poor touch-sensing resolution due to the large width of individual light beams employed. As a result, touches to the display by objects having a small footprint, such as a stylus, may not be sufficient to register as a touch on the display, for example because the object is too narrow to fully block an LED beam of light. Yet a further problem with LED touch screen input devices is that the miniaturization of this type of touch screen is not practical for small format applications. Again, the number and size of the components makes it very difficult if not unfeasible to adapt this technology to small format applications.
For the foregoing reasons, it can be appreciated that a need exists for a compact, inexpensive, and simple apparatus that may be used in a touch input device for a touch screen display system.